Plasma enhanced chemical vapor deposition (PECVD) is a useful way of depositing high quality amorphous silicon thin films on various substrates. One reason for that quality is that the resulting amorphous silicon contains a significant amount of hydrogen (about 5-10 atomic %). While such a hydrogen content is generally beneficial when fabricating devices from amorphous silicon, the hydrogen complicates the formation of polysilicon devices from PECVD deposited amorphous silicon when using laser crystallization. This is so since laser crystallization of hydrogenated amorphous silicon tends to cause potentially explosive hydrogen ablation from the amorphous silicon.
One known method of dehydrogenizing amorphous silicon is to anneal the amorphous silicon/substrate structure at about 450.degree. C. for several hours prior to laser crystallization. This method removes hydrogen from the amorphous silicon and thus enables the production of polysilicon using laser recrystallization without the problem of ablation. However, the characteristics of devices made from dehydrogenated amorphous silicon are not good for devices, whereas those of similar devices made from hydrogenated amorphous silicon are of device grade.
Thus in the prior art, the fabrication of hybrid amorphous silicon/polysilicon devices on the same substrate typically required a trade-off between the characteristics of the amorphous silicon devices and the polysilicon devices.
Thus, there exists a need for low substrate temperature methods of dehydrogenizing and crystallizing selected areas of an amorphous silicon layer. The usefulness of such methods would further increase if they enabled PECVD deposition, dehydrogenation, and crystallization in the same chamber.